This is a method and circuit for stretching each group of phase reversed binary bits in a series by one full bit to improve the transmission characteristics by lowering the harmonic content while increasing the signal content.
In scanning imaging systems, one method of achieving improved resolution performance is through the use of a technique called "Scophony Imaging". This technique is described in an Optical Engineering article, 24(1). 093-100 (Jan/Feb 1985), Scophony Spatial Light Modulator, by Richard Johnson, JeanMichael Guerin and Melvin E. Swanberg. In such image scanning systems each image element or "pixel" is represented by a binary bit. In a normal series of binary bits, one clock period is assigned to each succesive bit. For example, an ON bit is indicated by a positive voltage and an OFF bit is indicated by zero volts. A group of bits is a connected series of bits of the same state. Then, for example, in a bit stream where a group of two ON bits is followed by a group of two OFF bits, there will be two clock periods where the output voltage will be high, followed by two clock periods where the output voltage will be zero.
Application of phase reversal to Optical scanners is also described in the article referenced above. FIG. 13 and accompanying text shows phase reversal being used in optical image formation. This means that for each successive group, the ON voltage will first be positive and then negative. Thus, for example, for three successive groups of ON bits, the first will be represented by a positive voltage, the second by a negative voltage and the third represented by a positive voltage. The OFF bits will always be zero volts.
The highest primary signal frequency that can be represented by a bit stream is where single ON and OFF bits alternate. Using the system of phase reversal results in a reduction of the primary signal by a factor of two, but the waveform contains a high content of odd harmonics. For the same data rate, it is desirable to increase the amplitude of the information portion of the signal, and to decrease the harmonics of this signal.